Minimally invasive surgical techniques have emerged as an important trend within the field of surgery. Minimally invasive surgery differs from standard open surgery in that surgical procedures are performed through small incisions in the body under the guidance of endoscopy, fluoroscopy, ultrasound or other remote imaging techniques. Minimally invasive surgical techniques reduce the morbidity of surgical procedures and greatly accelerate patient recovery. In many cases minimally invasive surgical techniques also reduce the overall cost of surgery, especially by shortening the recovery period during which patients must stay in the hospital. The speedy recovery reduces the financial burden of surgery on the patients by allowing them to resume their normal lives and their work more quickly. The widespread adoption of minimally invasive surgical techniques results in tremendous benefits not only for the individual patients, but also for society as a whole.
Many established surgical procedures have been converted from open surgical techniques to minimally invasive surgical techniques. One of the earliest procedures to benefit from this trend was arthroscopic knee surgery. The benefits of arthroscopic surgery to the patient in terms of decreased morbidity and faster recovery were at once evident and the procedure was quickly adopted, almost entirely replacing open surgery for diagnosis of knee injuries and meniscectomy or removal of torn cartilage. As the instruments and techniques for arthroscopic surgery improved, more complex procedures, such as repair of torn ligaments and tendons, also became possible.
Many other surgical procedures for both diagnostic and therapeutic purposes have been converted to minimally invasive surgical techniques through the use of endoscopes. One of the most recent procedures that has been successfully converted to minimally invasive surgical techniques by use of the laparoscope is cholecystectomy or gallbladder removal.
One of the great challenges facing minimally invasive surgery is the advancement of minimally invasive surgical techniques into the area of cardiac surgery. Certain cardiac surgery procedures that previously were only possible through open chest surgery have already been converted to minimally invasive surgical techniques. For example, catheter techniques have been developed for occlusion of patent ductus arteriosus or atrial septal defects and for valvuloplasty of stenotic aortic or mitral valves. Instruments and techniques have also been developed for endoscopic approaches to the heart, allowing more complex cardiac surgical procedures to be performed through minimally invasive surgical techniques. One such procedure that could benefit from minimally invasive surgical techniques is the replacement of a stenotic or insufficient mitral valve. Several techniques for closed chest mitral valve replacement surgery are described in co-pending patent application, Ser. No.08/163,241, filed Dec. 6, 1993, the complete disclosure of which is incorporate herein by reference.
One of the important challenges in minimally invasive surgical techniques is that of placing sutures in the tissue at the operating site and applying properly tied suture knots through the narrow access of an endoscopic cannula or other equally restrictive access passage. Two different approaches are commonly used in tying sutures in endoscopic surgery. These can be classified generally as intracorporeal knot tying techniques for tying sutures at the surgical site within the body and extracorporeal knot tying techniques which allow knots to be tied in the sutures outside of the body then transferred to the surgical site using a knot pusher.
Intracorporeal knot tying can be performed using endoscopic graspers or forceps to manipulate the sutures in a technique similar to instrumented knot tying in conventional surgery. Alternatively, specialized intracorporeal knot tiers can be used. Various intracorporeal knot tiers are shown in U.S. Pat. Nos. 5,234,443 to Phan et al., 4,641,652 to Hutterer et al. and 5,281,236 to Bagnato et al. Tying sutures using a graspers or an intracorporeal knot tier is difficult and tedious compared with standard bimanual methods of surgical knot tying. Using intracorporeal knot tiers usually requires specialized training in operating the instrument and, even in the hands of the most skilled operators, usually requires more time than standard knot tying techniques. In procedures where few knots have to be tied, where access to the surgical site is difficult or where the length of the procedure is not critical, intracorporeal knot tying may be the method of choice.
However, for closed chest mitral valve replacement, the complexity and time consumption of using intracorporeal knot tying techniques can be prohibitive. Surgical replacement of a diseased mitral valve can involve tying up to twenty individual multiple-throw suture knots, with up to 4 to 5 throws per suture. The rate of post surgical complications in cardiac procedures rises proportionally to the length of time that the patient must spend on cardiopulmonary bypass. Therefore, it is extremely important to keep the duration of the procedure as short as possible.
Experienced surgeons can be very deft at standard bimanual methods of surgical knot tying. In time-sensitive procedures it is best to take advantage of this practiced and well honed knot tying skill, rather than to try to retrain the surgeon to use complex intracorporeal knot tying techniques. Some knot pushers are designed specifically to take advantage of this prior skill by allowing the surgeon to form the suture knots extracorporeally, then use the knot pusher to transfer the knots to the surgical site and tighten them in place. A well designed knot pusher allows the surgeon to use a knot tying technique that closely mimics the standard bimanual knot tying technique and does not add undue complication to the procedure.
A common type of surgical knot pusher is made with a C-shaped loop on the distal end of an elongated shaft, as exemplified in U.S. Pat. No. 3,871,379 to Clarke. The opening of the C faces distally from the shaft and the opening is sized to pass the desired size of suture. These devices are used by first passing the suture through the tissue to be tied and bringing both ends of the suture out through the surgical entry point so that a knot can be tied extracorporeally. The C-shaped loop is then placed over the knot and is used to slide the knot down the suture to the surgical site. The knot may then be tightened by pulling on the suture ends. This type of knot pusher has several disadvantages. The knot pusher must be reloaded onto the suture thread each time another throw is added to the suture knot. This adds time and complexity to the tying technique. In many cases, the orientation of the C-shaped loop on the knot pusher prevents the knot from being pushed directly up to the tissue that is to be sutured. This can leave a bit of slack in the suture that would be a severe problem in valve replacement surgery because it could cause the replacement valve to loosen and potentially displace from its proper position in the heart or could lead to perivalvar leaks. The open gap of the C-shaped loop can accidentally drop the suture while pushing the knot down if it is not carefully handled. This can be very frustrating to the surgeon because the knot pusher will have to be rethreaded, which is much more difficult once the knot is halfway down the suture and within the body cavity. Also, the knot pusher has no means to insure that the knot remains centered on the knot pusher. The surgeon must carefully maintain equal tension on both ends of the suture or the knot will slide sideways out of the C-shaped loop. While this type of knot pusher works well with monofilament sutures, it has been found to be ineffective and difficult to use for braided sutures which are the type often preferred for valve replacement surgery. This is due to the fact that the narrow knot pushing edge within the C-shaped loop places too much pressure against the knot, which tends to make the knot lock up rather than sliding along the suture.
Another type of knot pusher has a pair of opposing grooves on the head of the knot pusher with a fiat surface between them. Examples of this type of knot pusher can be seen in U.S. Pat. Nos. 5,234,444 to Christoudias and 5,217,471 to Burkhart. The flat surface between the grooves allows the device to push the knot directly against the tissue that is being sutured and it separates the two ends of the suture so that the tension to tighten the knot acts parallel to the tissue surface, which more effectively tightens the knot than pulling the sutures perpendicular to the tissue surface. However, these knot pushers have the disadvantages that they must be reloaded onto the suture every time another throw is added to the knot and they are even more prone to dropping knots than the devices previously described.
A number of surgical knot pushers have been designed to overcome the problem of dropping the knot while transporting it to the surgical site. In general, this type of knot pusher has a pair of eyelets on opposite sides of the head of the device. Examples of this type of knot pusher can be seen in U.S. Pat. Nos. 5,176,691 to Pierce and 5,192,287 to Fournier. The two eyelets are very effective at avoiding dropping the knot and at keeping the knot properly centered in front of the device. The disadvantage of having two eyelets is that it makes it more difficult to thread the device onto the ends of the sutures. In addition, each time another throw is added to the knot, at least one end of the suture must be unthreaded from the eyelet, then rethreaded after the knot is made. This adds undue time and complexity to the knot tying procedure.
A few devices have been made with a single eyelet or passage through the head of the knot pusher. Examples of these can be found in U.S. Pat. Nos. 4,602,635 to Mulhollan et al., 5,292,327 to Dodd et al., 5,282,809 to Kammerer et al. and 5,217,470 to Weston. Invariably, this type of knot pusher has asymmetrical paths for the two ends of the suture, which results in uneven tension on the suture at the knot. The preferred suture knot for securing a replacement heart valve, which is a series of square knots, cannot be properly tied unless the two ends of the suture can be pulled with even tension. Therefore, this type of single eyelet knot pusher is not well suited for suturing replacement heart valves and is more useful for procedures that call for a slip knot, such as a fisherman's knot, Roeder knot, multiple half hitches or another type of suture knot that can be applied asymmetrically.
One interesting variation of the single eyelet knot pusher can be seen in U.S. Pat. No. 5,269,791 to Mayzels et al. In order to make the device easier to thread onto the suture, the eyelet has been replaced with a tapered metal spiral. The last turn of the spiral is made with a diameter larger than the suture material, but smaller than a knot in the same suture. The suture is loaded onto the knot pusher by placing the suture into the proximal turn of the spiral and winding it around the device until the suture is in the center of the spiral. The present inventor has found that this technique is not easy to practice in a surgical setting and that the device is not immune from dropping or tangling knots.
It should be noted that another subgenre of knot pushers, sometimes referred to as an endo loop, is made to deliver a pretied ligation loop to a remote surgical site. An example of such a device can be seen in U.S. Pat. No. 5,242,459 to Buelna. Because these devices deliver a closed loop of suture material, they are only useful for ligating vessels and, then, only when the vessel has already been severed. They cannot be used for ligating a vessel before it is severed or for approximating tissues. Therefore, they would be of little use in mitral valve replacement surgery.
Another common type of surgical knot pusher is exemplified in U.S. Pat. No. 5,257,637 to El Gazayerli. This knot pusher has a pair of opposing jaws very much like a pair of endoscopic forceps. The jaws have slots on their distal ends and one of the jaws pivots relative to the other. When the jaws are closed, the slotted ends can be used to push a knot through a cannula or a lumen in an endoscope. Once the jaws exit the distal end of the cannula, they can be separated. This effectively makes the head of the knot pusher wider so that, when the ends of the sutures are pulled, the tension on the knot is applied parallel to the tissue surface, which is more effective for tightening the knot. This device is most useful when a wider knot pusher is desired, but the only access to the surgical site is through a narrow cannula or other narrow opening. However, this type of knot pusher is difficult to use because it must be reloaded onto the suture every time another throw is added to the knot. As it is described in the patent, only one jaw of this knot pusher pivots, so the paths of the two ends of the suture are somewhat asymmetrical when the jaws are open. A later improvement to this device, not described in the patent, solves this problem by making both jaws of the knot pusher pivot symmetrically.
In general, the above-described existing knot pusher devices have been found to be suitable for advancing knots that are tied in braided suture material, which is significant because the preferred suture material for mitral valve replacement surgery is braided nylon, dacron or polyester sutures. This is due to the fact that, in each of these devices, the paths of the sutures through the device include corners or other abrupt changes in direction that cause significant amounts of friction as the knot is advanced. Monofilament sutures are smoother so there is less friction between the suture strands or between the strands and the knot pusher. Monofilament sutures are also relatively stiffer than braided sutures of the same size, so they tend to round out the corners in the suture path through the device. Braided sutures, on the other hand, have a rougher surface texture which causes more friction between the suture strands and against the device. Also, because the more flexible braided sutures conform to every curve in the path, they are more sensitive to corners or other abrupt changes in direction. When a badly placed corner in a knot pusher presses against a knot in a braided suture, it tends to lock the knot so that it will not slide. This jams the knot pusher, slowing down the procedure and frustrating the surgeon.
Another detail of construction that is significant in mitral valve replacement surgery is that, when the replacement valve used is a mechanical valve as opposed to a bioprosthesis, the knot pusher must be made so that no metal parts can possibly come in contact with the mechanical replacement valve. This is because mechanical heart valves are made with highly polished surfaces that may also be coated with a hemocompatible coating such as pyrolytic carbon to reduce hemolysis and platelet attachment. Any disturbance in the surface of the valve or the coating could become a locus for increased hemolysis, thrombogenisis or platelet attachment and thrombosis. This could lead to possibly fatal post-surgical complications. Thus, at least the leading edge of the knot pusher should be made of plastic or another material that will not damage the surface of the replacement valve if there is accidental contact between them during installation. Many of the prior art knot pushing devices are impractical for constructing out of plastic because of their complex geometries or a need for high strength in the moving parts. Therefore, they would not be suitable for use in valve replacement surgery.